Technical improvements in digital, cellular telephones using radio transmission have produced a problem for users of such cellular telephones who wear hearing aids. Early cellular telephone system implementations used a system called analog transmission and were not a serious problem. Each user had an exclusive radio channel. The subsequent need for more channels resulted in a technical change in the method of transmission. To obtain better utilization of the radio spectrum, systems were devised to gather signals during short periods of time and transmit the signals in much shorter bursts of radio energy. At the receiving end, this burst was expanded to its original length of time, resulting in a signal which sounded continuous. During the time between bursts, other callers could be using the same channel. To accomplish this, the radio transmitter had to be turned off between bursts. This intermittent radio transmission interferes with many electronic devices. While the analog cellular telephones also interacted with these devices, because it transmitted continuously, it only made a momentary disruption at the beginning and end of the call. If the information stream did not interact with the intended use of the device, it produced no real harm.
On the other hand, the improved transmission system turned the transmitter on and off at a rate that produced disruptions at a frequency that was quite audible to users of hearing aids. The rate of these disruptions for practical reasons was in the lower audible range. Such systems need to operate at pulse rates between tens of pulses per second to a few hundred pulses per second. There are at this time, systems pulsing at 50 times per second and at 217 times per second. While in use, the radio transmitter in the telephone handset must necessarily be in close proximity to the hearing aid, therefore, there is an intense radio frequency signal intercepting the hearing aid. This produces disturbances in the electronics of conventional hearing aids, which make their use impossible.
The problem in the hearing aid was the result of the radio frequency signals interacting with the semiconductor components in the hearing aid that are necessary for its operation. There are many avenues that this disruptive RF signal can enter the hearing aid circuitry. The conventional prior art methods ameliorating this problem are to prevent the entry of the radio signal to the sensitive portions of the hearing aid circuitry. Common approaches include shielding, reducing the sensitivity to radio frequency pick up by arranging the wiring and attenuating the propagation of the radio frequency as it approaches demodulating components in the hearing aid. These helped the hearing aid's performance, but frequently left an annoying residual buzz.
While the previously mentioned precautions are necessary, if a way could be devised to reduce the residual interference, the quality of the transmission could be improved.